Honeycomb filter

ABSTRACT

A honeycomb filter includes a plugged honeycomb structure body which has cell rows arranged along one direction in a cross section of the honeycomb structure body and including a first cell row constituted of inflow cells and a second cell row including outflow cells. A width P 1  (mm) of the first cell row, a width P 2  (mm) of the second cell row and a curvature radius R (μm) of a curved shape of corner portions of a polygonal shape of each cell satisfy relations of Equations (1) and (2) below: Equation (1): 2≤100−(P 1 /P 2 ×100)≤50, and Equation (2): 0.4≤(R/1000)/((P 1 +P 2 )/2)×100≤20.

The present application is an application based on JP 2017-095953 filed on May 12, 2017 with Japan Patent Office, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a honeycomb filter, and more particularly, it relates to a honeycomb filter which is capable of effectively inhibiting leakage of particulate matter such as soot and inhibiting rise of pressure loss.

Description of the Related Art

In various industries, internal combustion engines are used as power sources. On the other hand, exhaust gases emitted from the internal combustion engines during combustion of fuel include particulate matter such as soot and ash. For example, regulations on removal of the particulate matter to be emitted from a diesel engine have become stricter worldwide, and as a filter to remove the particulate matter, a honeycomb filter having a honeycomb structure is used. Hereinafter, the particulate matter will occasionally be referred to as “PM”. The PM is an abbreviation for “the particulate matter”.

Heretofore, as the honeycomb filter to remove the PM, there has been suggested a honeycomb filter including a honeycomb structure body having porous partition walls which define a plurality of cells, and a plugging portion to plug either one of end portions of each of the cells (e.g., see Patent Document 1).

Such a honeycomb filter has a structure in which the porous partition walls perform a function of a filter which removes the PM. Specifically, when an exhaust gas containing the PM flows into an inflow end face of the honeycomb filter, the PM is trapped by the porous partition walls to filter the exhaust gas, and then the purified exhaust gas is emitted from an outflow end face of the honeycomb filter. In this way, the PM in the exhaust gas can be removed.

In the honeycomb filter, a shape of the cells defined by the partition walls has variously been studied, and there has been suggested, for example, a honeycomb filter in which cells opened on an inflow end face side (hereinafter occasionally referred to as “inflow cells”) are formed in an octagonal shape (e.g., see Patent Document 2). Furthermore, there has been studied, for example, a technology of increasing the number of the inflow cells to be larger than the number of cells opened on an outflow end face side (hereinafter occasionally referred to as “outflow cells”), thereby inhibiting rise of pressure loss.

Additionally, as to the honeycomb filter, arrangement of plugging portions to plug open ends of the cells has also variously been studied. For example, a honeycomb filter has been suggested in which eight inflow cells are arranged to surround a periphery of one outflow cell (e.g., see Patent Document 3).

In addition, as the honeycomb filter, there has been suggested a technology of forming the outflow cells so that regions corresponding to corner portions in a rectangular shape or a more polygonal shape are circularly formed (e.g., see Patent Document 4). In the honeycomb filter described in Patent Document 4, it is explained that the above constitution is employed, thereby increasing a heat capacity of the honeycomb filter, so that temperature rise during regeneration can be decreased.

[Patent Document 1] WO 2004/052502

[Patent Document 2] JP-A-2015-029939

[Patent Document 3] JP-A-2016-52635

[Patent Document 4] JP-A-2010-221159

SUMMARY OF THE INVENTION

In a honeycomb filter, inhibition of increase of pressure loss in an initial stage of use and during the use has heretofore been a large problem. An example of a factor which causes the increase of the pressure loss is increase of an airflow resistance of partition walls due to trapping of PM with the partition walls. Furthermore, as the factor which causes the increase of the pressure loss, pressure loss generated when an exhaust gas flows into the honeycomb filter or when the exhaust gas flows out from the honeycomb filter or pressure loss when the exhaust gas passes through cells also becomes the problem. Among these factors, it is considered that the increase of the airflow resistance when the PM is trapped by the partition walls is a larger factor in the increase of the pressure loss of the honeycomb filter.

It is considered that there are roughly two stages in the increase of the pressure loss when the PM is trapped by the partition walls. Initially, in a first stage, the PM penetrates into pores formed in the partition walls and is trapped, and parts of the pores of the partition walls are closed with the PM, thereby causing the rise of the pressure loss. It is considered that the first stage of the rise of the pressure loss occurs comparatively in the initial stage of the use of the honeycomb filter. Next, in a second stage, the PM is deposited on the surfaces of the partition walls, and a deposited layer of the PM causes the rise of the pressure loss. The second stage of the rise of the pressure loss is more moderate than the first stage of the rise of the pressure loss. Furthermore, it is considered that the rise of the pressure loss in the second stage occurs at time which is comparatively later than rise time of the pressure loss in the first stage.

The PM included in the exhaust gas includes incombustible particulate matter such as ash. When the honeycomb filter is continuously used, the ash is deposited on the surfaces of the partition walls, and the pressure loss of the honeycomb filter increases. Consequently, as a countermeasure to inhibit the increase of the pressure loss of the honeycomb filter, for example, a method of increasing a capacity for the ash to be deposited in the honeycomb filter is considered.

For example, when inflow cells are formed in an octagonal shape or the like, a surface area of the partition walls which define the inflow cells increases, and it is possible to increase the capacity for the ash to be deposited. However, in the countermeasure of only changing the shape of the inflow cells, when an amount of the ash to be generated increases, it is difficult to acquire a sufficient capacity for the ash to be deposited.

Furthermore, for example, when all the cells linearly arranged in one row are formed as the inflow cells and the number of the inflow cells is adjusted to be larger than the number of outflow cells, it is possible to increase the capacity for the ash to be deposited. However, in such a honeycomb filter, the number of the outflow cells noticeably decreases, and hence, there is the problem that a large back pressure is generated on an outflow end face side. Furthermore, when an amount of the ash to be generated increases, the number of the inflow cells further has to be increased, thereby causing the problem that the back pressure of the honeycomb filter further increases.

Additionally, in such a honeycomb filter as described in Patent Document 3, particulate matter such as soot is easily deposited on corner portions of inflow cells, and during actual use, cracks and the like are generated in the corner portions of the inflow cells, thereby causing the problem that the soot and the like leak out from corner portions of outflow cells.

In such a honeycomb filter as described in Patent Document 4, regions corresponding to corner portions of outflow cells are only formed in a circular shape, and hence, there is the problem that cracks and the like are easily generated among inflow cells.

The present invention has been developed in view of such problems of conventional technologies. According to the present invention, there is provided a honeycomb filter which is capable of effectively inhibiting leakage of particulate matter such as soot and inhibiting rise of pressure loss. In particular, there is provided a honeycomb filter which is capable of effectively inhibiting rise of pressure loss at the start of use and in an initial state of the use.

According to the present invention, there is provided a honeycomb filter as follows.

According to a first aspect of the present invention, a honeycomb filter is provided including:

a honeycomb structure body having porous partition walls arranged to surround a plurality of cells extending from an inflow end face to an outflow end face to form through channels for a fluid, and

a plugging portion disposed to plug either one of end portions of each of the cells on the side of the inflow end face or the side of the outflow end face,

wherein the honeycomb structure body has a plurality of cell rows in which two or more cells are linearly arranged along one direction, in a cross section of the honeycomb structure body which is perpendicular to an extending direction of the cells,

the plurality of cell rows include a first cell row and a second cell row,

the first cell row is a cell row constituted of inflow cells in which the plugging portions are arranged in end portions on the outflow end face side and which are opened on the inflow end face side,

the second cell row is a cell row of the cells linearly arranged along the one direction and including outflow cells in which the plugging portions are arranged in end portions on the inflow end face side and which are opened on the outflow end face side,

a width P1 (mm) of the first cell row and a width P2 (mm) of the second cell row satisfy a relation of Equation (1) mentioned below,

in the cross section perpendicular to the extending direction of the cells, each of the cells has a polygonal shape of which corner portions are formed in a curved shape of a curvature radius R, and

the width P1 (mm) of the first cell row, the width P2 (mm) of the second cell row and the curvature radius R (μm) satisfy a relation of Equation (2) mentioned below: 2≤100−(P1/P2×100)≤50, and  Equation (1): 0.4≤(R/1000)/((P1+P2)/2)×100≤20.  Equation (2):

According to a second aspect of the present invention, the honeycomb filter according to the above first aspect is provided, wherein an average value of the width P1 of the first cell row and the width P2 of the second cell row is from 0.5 to 2.7 mm.

According to a third aspect of the present invention, the honeycomb filter according to the above first or second aspects is provided, wherein the width P1 of the first cell row is from 0.3 to 2.7 mm.

According to a fourth aspect of the present invention, the honeycomb filter according to any one of the above first to third aspects is provided, wherein the width P2 of the second cell row is from 0.7 to 2.7 mm.

According to a fifth aspect of the present invention, the honeycomb filter according to any one of the above the first to fourth aspects is provided, wherein in the cross section perpendicular to the extending direction of the cells, a ratio N2/N1 of the number N2 of the second cell rows to the number N1 of the first cell rows is from 1/4 to 4.0.

According to a sixth aspect of the present invention, the honeycomb filter according to any one of the above first to fifth aspects is provided, wherein the second cell row is a cell row in which the inflow cells and the outflow cells are mixed.

According to a seventh aspect of the present invention, the honeycomb filter according to any one of the above first to fifth aspects is provided, wherein the second cell row is a cell row constituted of the outflow cells.

According to an eighth aspect of the present invention, the honeycomb filter according to any one of the above first to seventh aspects is provided, wherein in the cross section perpendicular to the extending direction of the cells, the first cell rows are arranged on both sides of the second cell row, respectively.

According to a ninth aspect of the present invention, the honeycomb filter according to the above eighth aspect is provided, wherein in the cross section perpendicular to the extending direction of the cells, the first cell rows and the second cell rows are alternately arranged in a direction perpendicular to the respective rows.

According to a tenth aspect of the present invention, the honeycomb filter according to any one of the above first to ninth aspects is provided, comprising two or more regions having different constitutions of the cell row in the cross section perpendicular to the extending direction of the cells, wherein the honeycomb structure body is present in at least a part of the regions.

According to an eleventh aspect of the present invention, the honeycomb filter according to any one of the above first to ninth aspects is provided, comprising a plurality of honeycomb structure bodies, wherein each of the honeycomb structure bodies is constituted of a pillar-shaped honeycomb segment, and side surfaces of a plurality of honeycomb segments are bonded to one another by a bonding layer.

A honeycomb filter of the present invention has a first cell row in which inflow cells are linearly arranged as two or more cells linearly arranged along one direction. Consequently, the honeycomb filter of the present invention is capable of acquiring a large capacity for ash to be deposited and effectively inhibiting rise of pressure loss. Furthermore, the honeycomb filter of the present invention is constituted to satisfy Equation (1) mentioned above, and hence, it is possible to inhibit decrease of a total open area of cells on the side of an outflow end face as compared to the side of an inflow end face, and it is also possible to effectively inhibit the rise of the pressure loss at the start of use and in an initial state of the use. Furthermore, in the honeycomb filter of the present invention, each cell has a constitution in which corner portions of a polygonal shape are formed in a curved shape of a curvature radius R. Then, the honeycomb filter is constituted to satisfy Equation (2) mentioned above, and hence, it is possible to effectively inhibit leakage of particulate matter such as soot from the honeycomb filter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view schematically showing a first embodiment of a honeycomb filter of the present invention and seen from the side of an inflow end face;

FIG. 2 is a plan view schematically showing the inflow end face of the honeycomb filter shown in FIG. 1;

FIG. 3 is a plan view schematically showing an outflow end face of the honeycomb filter shown in FIG. 1;

FIG. 4 is an enlarged plan view of an enlarged part of the inflow end face of the honeycomb filter shown in FIG. 2;

FIG. 5 is an enlarged plan view of an enlarged part of the outflow end face of the honeycomb filter shown in FIG. 3;

FIG. 6 is a cross-sectional view schematically showing a cross section taken along the A-A′ line of FIG. 4;

FIG. 7 is a cross-sectional view schematically showing a cross section taken along the B-B′ line of FIG. 4;

FIG. 8 is an enlarged plan view of an enlarged part of an inflow end face, schematically showing a second embodiment of the honeycomb filter of the present invention;

FIG. 9 is an enlarged plan view of an enlarged part of an outflow end face, schematically showing the second embodiment of the honeycomb filter of the present invention;

FIG. 10 is an enlarged plan view of an enlarged part of an inflow end face, schematically showing a third embodiment of the honeycomb filter of the present invention;

FIG. 11 is an enlarged plan view of an enlarged part of an outflow end face, schematically showing the third embodiment of the honeycomb filter of the present invention;

FIG. 12 is an enlarged plan view of an enlarged part of an inflow end face, schematically showing a fourth embodiment of the honeycomb filter of the present invention;

FIG. 13 is an enlarged plan view of an enlarged part of an outflow end face, schematically showing the fourth embodiment of the honeycomb filter of the present invention;

FIG. 14 is an enlarged plan view of an enlarged part of an inflow end face, schematically showing a fifth embodiment of the honeycomb filter of the present invention;

FIG. 15 is an enlarged plan view of an enlarged part of an outflow end face, schematically showing the fifth embodiment of the honeycomb filter of the present invention;

FIG. 16 is an enlarged plan view of an enlarged part of an inflow end face, schematically showing a sixth embodiment of the honeycomb filter of the present invention;

FIG. 17 is an enlarged plan view of an enlarged part of an outflow end face, schematically showing the sixth embodiment of the honeycomb filter of the present invention;

FIG. 18 is an enlarged plan view of an enlarged part of an inflow end face, schematically showing a seventh embodiment of the honeycomb filter of the present invention;

FIG. 19 is an enlarged plan view of an enlarged part of an outflow end face, schematically showing the seventh embodiment of the honeycomb filter of the present invention;

FIG. 20 is an enlarged plan view of an enlarged part of an inflow end face, schematically showing an eighth embodiment of the honeycomb filter of the present invention;

FIG. 21 is an enlarged plan view of an enlarged part of an outflow end face, schematically showing the eighth embodiment of the honeycomb filter of the present invention;

FIG. 22 is an enlarged plan view of an enlarged part of an inflow end face, schematically showing a ninth embodiment of the honeycomb filter of the present invention;

FIG. 23 is an enlarged plan view of an enlarged part of an outflow end face, schematically showing the ninth embodiment of the honeycomb filter of the present invention;

FIG. 24 is an enlarged plan view of an enlarged part of an inflow end face, schematically showing a tenth embodiment of the honeycomb filter of the present invention;

FIG. 25 is an enlarged plan view of an enlarged part of an outflow end face, schematically showing the tenth embodiment of the honeycomb filter of the present invention;

FIG. 26 is a plan view of an inflow end face, schematically showing another embodiment of the honeycomb filter of the present invention;

FIG. 27 is a plan view of an inflow end face, schematically showing still another embodiment of the honeycomb filter of the present invention;

FIG. 28 is a plan view of an inflow end face, schematically showing a further embodiment of the honeycomb filter of the present invention;

FIG. 29 is a perspective view schematically showing a still further embodiment of the honeycomb filter of the present invention and seen from the side of an inflow end face;

FIG. 30 is an enlarged plan view of an enlarged part of an inflow end face, schematically showing honeycomb filters of Example 22 and Example 23; and

FIG. 31 is an enlarged plan view of an enlarged part of an outflow end face, schematically showing the honeycomb filters of Example 22 and Example 23.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, description will be made as to embodiments of the present invention. However, the present invention is not limited to the following embodiments. Therefore, it should be understood that changes, improvements and the like are suitably addable to the following embodiments on the basis of ordinary knowledge of a person skilled in the art without departing from the gist of the present invention.

(1) Honeycomb Filter (First Embodiment)

As shown in FIG. 1 to FIG. 7, a first embodiment of a honeycomb filter of the present invention is a honeycomb filter 100 including a honeycomb structure body 4 having porous partition walls 1, and a plugging portion 5 disposed in either one of end portions of each of cells 2 formed in the honeycomb structure body 4. Here, FIG. 1 is a perspective view schematically showing a first embodiment of the honeycomb filter of the present invention and seen from the side of an inflow end face. FIG. 2 is a plan view schematically showing the inflow end face of the honeycomb filter shown in FIG. 1. FIG. 3 is a plan view schematically showing an outflow end face of the honeycomb filter shown in FIG. 1. FIG. 4 is an enlarged plan view of an enlarged part of the inflow end face of the honeycomb filter shown in FIG. 2. FIG. 5 is an enlarged plan view of an enlarged part of the outflow end face of the honeycomb filter shown in FIG. 3. FIG. 6 is a cross-sectional view schematically showing a cross section taken along the A-A′ line of FIG. 4. FIG. 7 is a cross-sectional view schematically showing a cross section taken along the B-B′ line of FIG. 4.

The partition walls 1 of the honeycomb structure body 4 are arranged to surround a plurality of cells 2 extending from an inflow end face 11 to an outflow end face 12 to form through channels for a fluid. That is, the plurality of cells 2 are defined by the porous partition walls 1. The plugging portion 5 is disposed to plug either one of the end portions of each of the cells 2 formed in the honeycomb structure body 4. Consequently, either one of the end portions of each of the plurality of cells 2 is plugged with the plugging portion 5 disposed at an open end of the cell on the side of the inflow end face 11 or the outflow end face 12. In the honeycomb filter 100 of the present embodiment, the porous partition walls 1 function as a filtering material to trap PM in an exhaust gas. Here, among the plurality of cells 2, the cells 2 in which the plugging portions 5 are arranged at the open ends on the side of the outflow end face 12 and which are opened on the side of the inflow end face 11 are defined as inflow cells 2 a. Furthermore, among the plurality of cells 2, the cells 2 in which the plugging portions 5 are arranged at the open ends on the side of the inflow end face 11 and which are opened on the side of the outflow end face 12 are defined as outflow cells 2 b.

The honeycomb structure body 4 has a plurality of cell rows in which two or more cells 2 are linearly arranged along one direction, in a cross section of the honeycomb structure body 4 which is perpendicular to an extending direction of the cells 2. Furthermore, the plurality of cell rows include a first cell row 15 and a second cell row 16 as described hereinafter. The first cell row 15 is a cell row constituted of the inflow cells 2 a in which the plugging portions 5 are arranged in end portions on the outflow end face 12 side and which are opened on the inflow end face 11 side. Furthermore, the second cell row 16 is a cell row of the cells 2 linearly arranged along one direction and including the outflow cells 2 b in which the plugging portions 5 are arranged in end portions on the inflow end face 11 side and which are opened on the outflow end face 12 side. It is to be noted that the second cell row 16 may be a cell row constituted only of the outflow cells 2 b or a cell row in which the outflow cells 2 b and the inflow cells 2 a are mixed. On the other hand, as described above, the first cell row 15 is the cell row constituted only of the inflow cells 2 a.

In the honeycomb filter 100 of the present embodiment, a width P1 of the first cell row 15 and a width P2 of the second cell row 16 satisfy a relation of Equation (1) mentioned below. In Equation (1) mentioned below, P1 indicates the width P1 (unit: mm) of the first cell row 15, and P2 indicates the width P2 (unit: mm) of the second cell row 16. In the honeycomb structure body 4 shown in FIG. 4 and FIG. 5, a side edge in measuring the width of each cell row is an intermediate position of a thickness of the partition wall 1 disposed at the side edge of each cell row. In this way, the side edges on both sides of each cell row are obtained, and a distance between two side edges is measured. The measured distance between the two side edges is considered as the width of each of the cell rows. 2≤100−(P1/P2×100)≤50  Equation (1):

Furthermore, according to the honeycomb filter 100 of the present embodiment, in the cross section perpendicular to the extending direction of the cells 2, corner portions 6 of a polygonal shape of each of the cells 2 are formed in a curved shape of a curvature radius R (μm). In FIG. 4 and FIG. 5, reference numeral 6 indicates the corner portions 6 formed in the curved shape in the shape of the cell 2 in the cross section perpendicular to the extending direction of the cells 2. Furthermore, the width P1 (mm) of the first cell row 15, the width P2 (mm) of the second cell row 16 and the curvature radius R (m) satisfy a relation of Equation (2) mentioned below. In Equation (2) mentioned below, R indicates the curvature radius R (unit: μm) of a curved region in each of the corner portions 6 of the cells 2. 0.4≤(R/1000)/((P1+P2)/2)×100≤20  Equation (2):

According to such a constitution, it is possible to inhibit rise of pressure loss of the honeycomb filter 100. Specifically, the honeycomb filter 100 of the present embodiment has the first cell row 15 in which the inflow cells 2 a are linearly arranged, and hence, it is possible to acquire a large capacity for ash to be deposited. Furthermore, the honeycomb filter 100 is constituted to satisfy Equation (1) mentioned above, and hence, the honeycomb filter has the constitution in which the width P1 of the first cell row 15 is smaller than the width P2 of the second cell row 16. Consequently, even when the honeycomb filter 100 has the first cell row 15, an open frontal area of the honeycomb filter on the outflow end face 12 side does not remarkably decrease as compared to the inflow end face 11 side. Therefore, according to the honeycomb filter 100 of the present embodiment, it is possible to effectively inhibit the rise of the pressure loss while acquiring the large capacity for the ash to be deposited. In particular, the honeycomb filter 100 of the present embodiment is capable of effectively inhibiting the rise of the pressure loss at the start of use and in an initial state of the use. Furthermore, the honeycomb filter 100 is constituted so that each of the cells 2 has the shape in which the corner portions 6 of the polygonal shape are formed into the curved shape of the curvature radius R. Additionally, the honeycomb filter is constituted to satisfy Equation (2) mentioned above, and hence, it is possible to effectively inhibit leakage of particulate matter such as soot from the honeycomb filter 100.

In Equation (1), when a value of “100−(P1/P2×100)” is less than 2, a ratio of the outflow cells 2 b to the inflow cells 2 a decreases. Consequently, when a small amount of soot is deposited from a state where any soot is not deposited on the partition walls 1, the rise of the pressure loss of the honeycomb filter 100 might increase. In Equation (1), when the value of “100−(P1/P2×100)” is in excess of 50, a sufficient capacity for the ash to be deposited cannot be acquired, and hence, the pressure loss noticeably increases when the ash is deposited. In Equation (1), the value of “100−(P1/P2×100)” is especially preferably 5 or more. Furthermore, the value is especially preferably 45 or less.

In Equation (2), when a value of “(R/1000)/((P1+P2)/2)×100” is less than 0.4, the soot or the like easily leaks out from the honeycomb filter 100. In Equation (2), when the value of “(R/1000)/((P1+P2)/2)×100” is in excess of 20, the pressure loss noticeably increases. In Equation (2), the value of “(R/1000)/((P1+P2)/2)×100” is especially preferably 1 or more. Furthermore, the value is especially preferably 15 or less.

In each of the cells 2, the curvature radius R of each of the corner portions 6 formed in the curved shape can be measured as follows. Initially, the inflow end face 11 and the outflow end face 12 of the honeycomb filter 100 are imaged with an image measuring instrument. Then, images of the imaged inflow end face 11 and outflow end face 12 are analyzed, thereby obtaining the curvature radius R of the corner portion 6. In a method of the image analysis, for example, “VM-2520 (tradename)” manufactured by Nikon Corporation is usable. The curvature radius R of the corner portion 6 of the cell 2 is obtainable by obtaining a radius (or a diameter) of an inscribed circle of the corner portions 6 in curve fitting to the corner portions 6 of the cell 2 by the above image analysis.

In the honeycomb filter 100 of the present embodiment, a cell row directing direction, i.e., the above-mentioned one direction may be an optional direction in the cross section of the honeycomb structure body 4 which is perpendicular to the extending direction of the cells 2, as long as two or more cells 2 are linearly arranged in the direction. However, when the width P1 of the first cell row 15 is compared with the width P2 of the second cell row 16, the respective cell rows are parallel cell rows extending in the same direction.

In the cross section of the honeycomb structure body 4 which is perpendicular to the extending direction of the cells 2, at least one row may be present as the first cell row 15. Furthermore, in the cross section of the honeycomb structure body 4 which is perpendicular to the extending direction of the cells 2, at least one row may be present as the second cell row 16. However, either one of the end portions of each of the plurality of cells 2 is plugged with the plugging portion 5 on the inflow end face 11 side or the outflow end face 12 side, and hence, all the cell rows that do not satisfy the conditions of the first cell row 15 correspond to the second cell rows 16.

An average value of the width P1 of the first cell row 15 and the width P2 of the second cell row 16 is preferably from 0.5 to 2.7 mm and further preferably from 0.7 to 2.0 mm. When the above average value is less than 0.5 mm, clogging of the cells 2 due to the depositing of the soot unfavorably occurs. Furthermore, when the above average value is in excess of 2.7 mm, the substantial number of the cells decreases, thereby increasing an amount of the soot to be deposited per cell 2, and the rise of the pressure loss is unfavorably caused.

The width P1 of the first cell row 15 is preferably from 0.3 to 2.7 mm and further preferably from 0.5 to 2.0 mm. When the width P1 of the first cell row 15 is less than 0.3 mm, the clogging of the cells 2 due to the depositing of the soot unfavorably occurs. Furthermore, when the width P1 of the first cell row 15 is in excess of 2.7 mm, the substantial number of the cells decreases, thereby increasing the amount of the soot to be deposited per cell 2, and the rise of the pressure loss is unfavorably caused.

The width P2 of the second cell row 16 is preferably from 0.7 to 2.7 mm and further preferably from 1.0 to 2.0 mm. When the width P2 of the second cell row 16 is less than 0.7 mm, the clogging of the cells 2 due to the depositing of the soot unfavorably occurs. Furthermore, when the width P2 of the second cell row 16 is in excess of 2.7 mm, the substantial number of the cells decreases, thereby increasing the amount of the soot to be deposited per cell 2, and the rise of the pressure loss is unfavorably caused.

In each of the first cell row 15 and the second cell row 16, there are not any special restrictions on the number of the cells 2 to be linearly arranged. However, in each of the cell rows, it is preferable that five or more cells 2 are linearly arranged, and it is further preferable that ten or more cells 2 are linearly arranged. It is to be noted that an upper limit of the number of the cells 2 to be linearly arranged is the number of all the cells 2 that are linearly present from one peripheral edge to the other peripheral edge of the honeycomb structure body 4.

In the cross section perpendicular to the extending direction of the cells 2, each of a number N1 of the first cell rows 15 and a number N2 of the second cell rows 16 may be at least one. In the honeycomb filter 100 of the present embodiment, a ratio N2/N1 of the number N2 of the second cell rows 16 to the number N1 of the first cell rows 15 is preferably from 1/4 to 4.0 and further preferably from 1/3 to 3.0. According to such a constitution, it is possible to effectively inhibit the rise of the pressure loss while acquiring the large capacity for the ash to be deposited. It is to be noted that when the above ratio N2/N1 is less than 1/4, the ratio of the number of the outflow cells 2 b to the number of the inflow cells 2 a decreases. Consequently, when the small amount of soot is deposited from the state where any soot is not deposited on the partition walls 1, the rise of the pressure loss of the honeycomb filter 100 might increase. Furthermore, when the above ratio N2/N1 is in excess of 4.0, the capacity for the ash to be deposited might decrease due to the decrease of the inflow cells 2 a.

In the cross section perpendicular to the extending direction of the cells 2, the first cell row 15 is disposed adjacent to the second cell row 16 via the partition wall 1. For example, as in the honeycomb filter 100 shown in FIG. 1 to FIG. 7, the first cell rows 15 may be arranged on both sides of the second cell row 16, respectively, in the cross section perpendicular to the extending direction of the cells 2. In the honeycomb filter 100, the first cell rows 15 and the second cell rows 16 are alternately arranged in a direction perpendicular to the respective rows in the cross section perpendicular to the extending direction of the cells 2. The honeycomb filter 100 having such a constitution is preferable in that it is possible to uniformly acquire the capacity for the ash to be deposited in any place of the honeycomb filter 100.

There are not any special restrictions on an overall shape of the honeycomb filter 100. An example of the overall shape of the honeycomb filter 100 shown in FIG. 1 is a round pillar shape in which the inflow end face 11 and the outflow end face 12 are round. Although not shown, another example of the overall shape of the honeycomb filter may be a pillar shape in which an inflow end face and an outflow end face have a substantially round shape such as an elliptic shape, a racetrack shape, or an oblong shape. Alternatively, the overall shape of the honeycomb filter may be a prismatic columnar shape in which an inflow end face and an outflow end face have a polygonal shape such as a quadrangular shape or a hexagonal shape.

A thickness of the partition walls 1 is preferably from 50 to 600 μm, further preferably from 100 to 500 μm, and especially preferably from 150 to 450 μm. When the thickness of the partition walls 1 is less than 50 μm, an isostatic strength of the honeycomb filter 100 might deteriorate. When the thickness of the partition walls 1 is in excess of 600 μm, the pressure loss might increase, and drop of an engine output or deterioration of a fuel efficiency might be caused. The thickness of the partition walls 1 is a value measured by a method of observing a cross section of the honeycomb filter 100 which is perpendicular to an axial direction with an optical microscope.

A porosity of the partition walls 1 is, for example, preferably from 20 to 90%, further preferably from 25 to 80%, and especially preferably from 30 to 75%. When the porosity of the partition walls 1 is less than 20%, the pressure loss of the honeycomb filter 100 might increase, and the drop of the engine output or the deterioration of the fuel efficiency might be caused. When the porosity of the partition walls 1 is 30% or more, the above problem is harder to occur. On the other hand, when the porosity of the partition walls 1 is in excess of 90%, the isostatic strength of the honeycomb filter 100 might deteriorate. When the porosity of the partition walls 1 is 75% or less, the above problem is harder to occur. It is to be noted that the porosity of the partition walls 1 is a value measured with a mercury porosimeter. An example of the mercury porosimeter is AutoPore 9500 (tradename) manufactured by Micromeritics Instrument Corp.

There are not any special restrictions on the original polygonal shape of the cells 2 as long as the corner portions 6 of the polygonal shape are formed in the curved shape of the curvature radius R. As described later, examples of the shape of the cells 2 include a quadrangular shape, a hexagonal shape and an octagonal shape.

There are not any special restrictions on a material constituting the partition walls 1, but from the viewpoints of strength, heat resistance, durability and the like, it is preferable that a main component is any type of ceramics of an oxide or a non-oxide, a metal, or the like. Specifically, it is considered that examples of ceramics include cordierite, mullite, alumina, spinel, silicon carbide, silicon nitride, and aluminum titanate. It is considered that examples of the metal include a Fe—Cr—Al based metal and metal silicon. It is preferable to use at least one selected from the group consisting of these materials as the main component. From the viewpoints of a high strength, a high heat resistance and the like, it is especially preferable to use at least one selected from the group consisting of alumina, mullite, aluminum titanate, cordierite, silicon carbide and silicon nitride, as the main component. Furthermore, from the viewpoints of a high thermal conductivity, a high heat resistance and the like, silicon carbide or a silicon-silicon carbide composite material is especially suitable. Here, “the main component” means a component constituting 50 mass % or more of the partition walls 1. The above component is included in the material constituting the partition walls 1 as much as preferably 70 mass % or more and further preferably 80 mass % or more.

It is preferable that a material of the plugging portions 5 is a material which is considered to be the preferable material of the partition walls. The material of the plugging portions 5 and the material of the partition walls 1 may be the same material or different materials.

In the honeycomb filter 100 of the present embodiment, an exhaust gas purifying catalyst may be loaded onto at least one of each of the surfaces of the partition walls 1 of the honeycomb structure body 4 and each of pores of the partition walls 1. According to this constitution, CO, NO_(x), HC and the like in the exhaust gas can be changed to harmless substances by a catalytic reaction. Furthermore, oxidation of the soot trapped in the partition walls 1 can be promoted.

When the catalyst is loaded onto the honeycomb filter 100 of the present embodiment, it is preferable that the catalyst includes at least one selected from the group consisting of an SCR catalyst, a NO_(x) absorber catalyst and an oxidation catalyst. The SCR catalyst is a catalyst to selectively reduce components to be purified. In particular, it is preferable that the SCR catalyst is a NO_(x) selectively reducing SCR catalyst to selectively reduce NO_(x) in the exhaust gas. Furthermore, an example of the SCR catalyst is a metal-substituted zeolite. Examples of a metal in the metal-substituted zeolite include iron (Fe) and copper (Cu). A suitable example of zeolite is a beta zeolite. Furthermore, the SCR catalyst may be a catalyst containing at least one selected from the group consisting of vanadium and titania, as a main component. Examples of the NO_(x) absorber catalyst include an alkali metal and an alkali earth metal. Examples of the alkali metal include potassium, sodium, and lithium. An example of the alkali earth metal is calcium. An example of the oxidation catalyst is a catalyst containing a noble metal. Specifically, it is preferable that the oxidation catalyst contains at least one selected from the group consisting of platinum, vanadium and rhodium.

(2) Honeycomb Filter (Second Embodiment to Tenth Embodiment)

Next, description will be made as to a second embodiment to a tenth embodiment of the honeycomb filter of the present invention with reference to FIG. 8 to FIG. 25. Here, each of FIG. 8 to FIG. 25 is an enlarged plan view of an enlarged part of an inflow end face or an outflow end face, schematically showing the second embodiment to the tenth embodiment of the honeycomb filter of the present invention.

In honeycomb filters 200, 300 and 400 of the second embodiment to the fourth embodiment shown in FIG. 8 to FIG. 13, a shape of the cells 2 is quadrangular, and the honeycomb filter is constituted to satisfy Equation (1) and Equation (2) mentioned above in the same manner as in the honeycomb filter 100 of the first embodiment (see FIG. 4 and the like). In particular, each of the honeycomb filters 200, 300 and 400 of the second embodiment to the fourth embodiment has a constitution in which a width P1 of a first cell row 15 is smaller than a width P2 of a second cell row 16. In each of the honeycomb filters 200, 300 and 400 of the second embodiment to the fourth embodiment, an arrangement of the first cell row 15 and the second cell row 16 is different from that in the honeycomb filter 100 of the first embodiment (see FIG. 4 and the like). Then, it is preferable that the honeycomb filter has a constitution similar to the honeycomb filter 100 of the first embodiment (see FIG. 4 and the like) except for the arrangement of the first cell row 15 and the second cell row 16.

As shown in FIG. 8 and FIG. 9, in the honeycomb filter 200 of the second embodiment, positions at which plugging portions 5 are to be arranged in the second cell row 16 are different from those in the second cell row of the honeycomb filter of the first embodiment. Specifically, in the honeycomb filter 200 of the second embodiment, a cell row in which inflow cells 2 a and outflow cells 2 b are alternately arranged is present also in a direction perpendicular to an extending direction of the first cell row 15 and the second cell row 16. On the other hand, in the honeycomb filter 100 of the first embodiment shown in FIG. 4 and FIG. 5, in two second cell rows 16 arranged via the first cell row 15, the arrangement positions of the plugging portions 5 are shifted as much as a half pitch. In the honeycomb filter 200 of the second embodiment, a row of the cells 2 in which the plugging portions are not linearly arranged is present also in a longitudinal direction of a paper surface of each of FIG. 8 and FIG. 9, in the same manner as in the first cell row 15. Consequently, in the honeycomb filter 200, the first cell rows 15 can be arranged along both of longitudinal and lateral axes when necessary. On the other hand, for example, when the cell row in the longitudinal direction of the paper surface of each of FIG. 8 and FIG. 9 does not have to be adjusted in the width P1 similar to that of the first cell row 15, the cells 2 may be arranged as in the honeycomb filter 100 shown in FIG. 4 and FIG. 5 or the honeycomb filter 200 shown in FIG. 8 and FIG. 9.

As shown in FIG. 10 and FIG. 11, in the honeycomb filter 300 of the third embodiment, as to the first cell row 15 having a constitution in which inflow cells 2 a are linearly arranged, two first cell rows are continuously arranged in a direction perpendicular to the first cell row 15. In this way, the first cell rows 15 and the second cell rows 16 do not have to be alternately arranged in a direction perpendicular to respective rows. The honeycomb filter 300 having this constitution has a cell row in which plugging portions are linearly arranged in all the cells, and hence, strength during canning of the honeycomb filter 300 is easily acquired. Here, the canning means storage of the honeycomb filter in a case such as a metal case.

As shown in FIG. 12 and FIG. 13, the honeycomb filter 400 of the fourth embodiment is the honeycomb filter 400 having the first cell row 15 and the second cell row 16 extending in a right-left direction (e.g., a lateral direction) of a paper surface of FIG. 12, and the first cell row 15 and the second cell row 16 extending in an upward-downward direction (e.g., a longitudinal direction) of the paper surface of FIG. 12. The first cell row 15 and the second cell row 16 extending in the right-left direction of the paper surface have a constitution in which the width P of the first cell row 15 is smaller than the width P2 of the second cell row 16. Furthermore, the first cell row 15 and the second cell row 16 extending in the upward-downward direction of the paper surface have a constitution in which a width P1′ of the first cell row 15 is smaller than a width P2′ of the second cell row 16. Then, the honeycomb filter 400 of the fourth embodiment is constituted to satisfy Equation (1) and Equation (2) mentioned above in respective longitudinal and lateral cell rows of the paper surface. In the honeycomb filter 400 having this constitution, an arrangement in the longitudinal direction can be the same as an arrangement in the lateral direction, and a permissible range as to directionality in arrangement of the honeycomb filter 400 preferably enlarges.

In honeycomb filters 500, 600, 700 and 800 of a fifth embodiment to an eighth embodiment shown in FIG. 14 to FIG. 21, cells 22 defined by partition walls 21 have a substantially quadrangular shape and a substantially octagonal shape. The substantially quadrangular shape is a shape in which corner portions of a quadrangular shape are formed in a curved shape, and the substantially octagonal shape is a shape in which corner portions of an octagonal shape are formed in a curved shape. Hereinafter, the substantially quadrangular shape in which the corner portions of the quadrangular shape are formed in the curved shape will occasionally be referred to simply as “the quadrangular shape”. Furthermore, the substantially octagonal shape in which the corner portions of the octagonal shape are formed in the curved shape will occasionally be referred to simply as “the octagonal shape”. Each of the honeycomb filters 500, 600, 700 and 800 of the fifth embodiment to the eighth embodiment is constituted to satisfy Equation (1) mentioned above, and to satisfy Equation (2) mentioned above when a curved region in each of the corner portions of the cells 22 have a curvature radius R.

In the honeycomb filters 500, 600, 700 and 800 of the fifth embodiment to the eighth embodiment, quadrangular cells 22 and octagonal cells 22 are alternately formed in a cross section of a honeycomb structure body 24 which is perpendicular to an extending direction of the cells 22. Each of the honeycomb filters 500, 600, 700 and 800 of the fifth embodiment to the eighth embodiment also has a constitution in which a width P1 of a first cell row 35 is smaller than a width P2 of a second cell row 36. It is preferable that the honeycomb filters 500, 600, 700 and 800 of the fifth embodiment to the eighth embodiment have a constitution similar to the honeycomb filter 100 (see FIG. 4 and the like) of the first embodiment except for the shape of the cells 22 and arrangement of the first cell row 35 and the second cell row 36.

Here, description will be made as to a method of measuring the width P1 of the first cell row 35 and the width P2 of the second cell row 36 in the honeycomb filters 500, 600, 700 and 800 of the fifth embodiment to the eighth embodiment shown in FIG. 14 to FIG. 21, with reference to FIG. 14 and FIG. 15. Initially, in the honeycomb filter 500 shown in FIG. 14 and FIG. 15, a cell row constituted of inflow cells 22 a in which plugging portions 25 are arranged in end portions on the side of an outflow end face 32 and which are opened on the side of an inflow end face 31 is defined as the first cell row 35. Furthermore, in cell rows in which the cells 22 are arranged along one direction, a cell row including outflow cells 22 b is defined as the second cell row 36. To measure the width of each cell row, initially, when the first cell row 35 denoted with reference numeral 35 is defined as “a measurement target cell row”, a cell 22 x disposed on an innermost side of the cell row is found from the cells 22 constituting the measurement target cell row. Next, as to the cell row disposed adjacent to this measurement target cell row, a cell 22 y disposed on an innermost side of the cell row is found from the cells 22 constituting the adjacent cell row. Then, an intermediate position between the cell 22 x and the cell 22 y in a direction perpendicular to the extending direction of the cell rows is defined as a side edge of “the measurement target cell row” on one side. By the above-mentioned method, side edges on both sides of “the measurement target cell row” are obtained and a distance between the two side edges is measured. The measured distance between the two side edges is considered as a width of “the measurement target cell row”.

The honeycomb filters 500, 600, 700 and 800 of the fifth embodiment to the eighth embodiment shown in FIG. 14 to FIG. 21 are honeycomb filters which are effective when an amount of soot in an exhaust gas is large and an amount of the soot to be deposited increases. In other words, these embodiments are suitable when it is more necessary to inhibit rise of pressure loss in a state where the soot is deposited than to inhibit rise of pressure loss when any soot is not deposited.

It is to be noted that the honeycomb filter 800 of the eighth embodiment shown in FIG. 20 and FIG. 21 is a honeycomb filter of a segmented structure which will be described later. Consequently, a structure of the cells 22 shown in FIG. 20 and FIG. 21 shows a part of an end face of one honeycomb segment constituting the honeycomb filter of the segmented structure.

In honeycomb filters 900 and 1000 of a ninth embodiment and a tenth embodiment shown in FIG. 22 to FIG. 25, a shape of cells 42 defined by partition walls 41 is substantially hexagonal. The substantially hexagonal shape is a shape in which corner portions of a hexagonal shape are formed in a curved shape. Hereinafter, the substantially hexagonal shape in which the corner portions of the hexagonal shape are formed in the curved shape will occasionally be referred to simply as “the hexagonal shape”. Each of the honeycomb filters 900 and 1000 of the ninth embodiment and the tenth embodiment is constituted to satisfy Equation (1) mentioned above and to satisfy Equation (2) mentioned above when a curved region in each of the corner portions of the cells 42 has a curvature radius R. It is to be noted that FIG. 22 to FIG. 25 are schematic views to explain arrangements of the hexagonal cells 42 in the honeycomb filters 900 and 1000 of the ninth embodiment and the tenth embodiment, and hence, the curved regions in the corner portions of the hexagonal cells 42 are omitted from the drawing.

The honeycomb filters 900 and 1000 of the ninth embodiment and the tenth embodiment have a constitution in which a width P1 of a first cell row 55 is smaller than a width P2 of a second cell row 56 in a cross section of a honeycomb structure body 44 which is perpendicular to an extending direction of the cells 42. FIG. 22 to FIG. 25 schematically show only the shape of the cells 42 defined by the partition walls 41. FIG. 22 to FIG. 25 show the partition walls 41 by straight lines, and show a thickness of the partition walls 41 in an abstracted state.

In the honeycomb filters 900 and 1000 of the ninth embodiment and the tenth embodiment shown in FIG. 22 to FIG. 25, during canning, uniformity of strength is achievable not only in longitudinal and lateral directions of each paper surface but also in a circumferential direction.

Description will be made as to a method of measuring the width P1 of the first cell row 55 and the width P2 of the second cell row 56 in the honeycomb filters 900 and 1000 of the ninth embodiment and the tenth embodiment shown in FIG. 22 to FIG. 25, with reference to FIG. 22 and FIG. 23. Initially, in the honeycomb filter 900 shown in FIG. 22 and FIG. 23, a cell row constituted of inflow cells 42 a in which plugging portions 45 are arranged in end portions on the side of an outflow end face 52 and which are opened on the side of an inflow end face 51 is defined as the first cell row 55. Furthermore, in cell rows in which the cells 42 are arranged along one direction, a cell row including outflow cells 42 b is defined as the second cell row 56. A side edge in measuring the width of each cell row is an intermediate position between an inwardly dented region and an outwardly projecting region in each of side edges of the respective cell rows. In this way, the side edges of each cell row on both sides are obtained and a distance between the two side edges is measured. The measured distance between the two side edges is considered as the width of the cell row.

(3) Honeycomb Filter (Other Embodiment)

Next, description will be made as to the other embodiments of the honeycomb filter of the present invention with reference to FIG. 26 to FIG. 29. Here, FIG. 26 is a plan view of an inflow end face, schematically showing another embodiment of the honeycomb filter of the present invention. FIG. 27 is a plan view of an inflow end face, schematically showing still another embodiment of the honeycomb filter of the present invention. FIG. 28 is a plan view of an inflow end face, schematically showing a further embodiment of the honeycomb filter of the present invention. FIG. 29 is a perspective view schematically showing a still further embodiment of the honeycomb filter of the present invention and seen from the side of an inflow end face.

In a honeycomb filter 2000 shown in FIG. 26, each of ranges of four regions in four corners of an inflow end face 11 of the honeycomb filter 2000 corresponds to a honeycomb structure body 4 which satisfies characteristics of the present invention. That is, in FIG. 26, the honeycomb structure body 4 of the range surrounded with a bold line and denoted with reference numeral 4 is constituted to satisfy Equation (1) and Equation (2) mentioned above. The honeycomb filter 2000 shown in FIG. 26 is effective for, for example, a case where an exhaust gas flows, in a concentrated manner, through a central portion of the honeycomb filter 2000 which is surrounded with a broken line. It is to be noted that in the honeycomb filter 2000 shown in FIG. 26, a range other than the range surrounded with the bold line and denoted with the reference numeral 4 does not have to satisfy Equation (1) mentioned above.

In a honeycomb filter 2100 shown in FIG. 27, a 1/4 fan-shaped range of the lower right of a paper surface corresponds to a honeycomb structure body 4 which satisfies the characteristics of the present invention, in an inflow end face 11 of the honeycomb filter 2100. That is, in FIG. 27, the honeycomb structure body 4 of the fan-shaped range surrounded with a bold line and denoted with reference numeral 4 is constituted to satisfy Equation (1) and Equation (2) mentioned above. Thus, in the honeycomb filter, unevenness might occur in a situation where particulate matter such as ash is deposited, in accordance with a layout in using the honeycomb filter, uneven flow of an exhaust gas, and the like. Consequently, as in the honeycomb filter 2100 shown in FIG. 27, the whole region of the end face of the honeycomb filter 2100 does not have to satisfy Equation (1) mentioned above. For example, in the honeycomb filter 2100, it is possible to effectively inhibit rise of pressure loss while acquiring a large capacity for the ash to be deposited, in accordance with the layout in using the honeycomb filter, the uneven flow of the exhaust gas, and the like. The present embodiment is effective for, for example, a case where the exhaust gas flows, in a concentrated manner, through a portion of the honeycomb filter 2100 which is surrounded with a broken line.

In a honeycomb filter 2200 shown in FIG. 28, a central portion of an inflow end face 11 of the honeycomb filter 2200 which is surrounded with a bold line corresponds to a honeycomb structure body 4 which satisfies the characteristics of the present invention. The honeycomb filter 2200 shown in FIG. 28 is effective for, for example, a case where an exhaust gas flows less in the vicinity of a circumferential portion.

A honeycomb filter 3000 shown in FIG. 29 is the honeycomb filter 3000 including honeycomb structure bodies 4, and a plugging portion 5 disposed in either one of end portions of each of cells 2 formed in the honeycomb structure bodies 4. Especially in the honeycomb filter 3000, each of the honeycomb structure bodies 4 is constituted of a pillar-shaped honeycomb segment 64, and side surfaces of a plurality of honeycomb segments 64 are bonded to one another by a bonding layer 65. That is, in the honeycomb filter 3000 of the present embodiment, each of the individual honeycomb segments 64 constituting the honeycomb filter 3000 of a segmented structure corresponds to the honeycomb structure body 4 in the honeycomb filter 3000. Here, “the honeycomb filter of the segmented structure” is a honeycomb filter having a constitution in which a plurality of individually prepared honeycomb segments 64 are bonded. It is to be noted that the honeycomb filter 100 in which the partition walls 1 of the honeycomb structure body 4 are all monolithically formed as shown in FIG. 1 to FIG. 7 will occasionally be referred to as “a monolithic honeycomb filter”. The honeycomb filter of the present invention may be “the honeycomb filter of the segmented structure” or “the monolithic honeycomb filter”.

In the honeycomb filter 3000, it is preferable that at least one of the honeycomb segments 64 has a constitution similar to the honeycomb structure body of the honeycomb filter of the hitherto described first embodiment. Specifically, at least one of the honeycomb segments 64 has a plurality of cell rows in which two or more cells 2 are linearly arranged along one direction. Then, the plurality of cell rows include a first cell row constituted of inflow cells 2 a, and a second cell row including outflow cells 2 b. Furthermore, at least one of the honeycomb segments 64 is constituted to satisfy Equation (1) and Equation (2) mentioned above. Also in the honeycomb filter 3000, technological effects similar to those of the honeycomb filter of the hitherto described first embodiment are obtainable. The plurality of honeycomb segments 64 may have the same cell structure, or may have different cell structures.

It is preferable that a circumferential wall 3 in the honeycomb filter 3000 is a circumference coating layer made of a circumference coating material. The circumference coating material is a coating material which is coated on a circumference of a bonded body obtained by bonding the plurality of honeycomb segments 64, to form the circumference coating layer. Furthermore, in the bonded body in which the plurality of honeycomb segments 64 are bonded, it is preferable that a circumferential portion of the bonded body is ground and the above-mentioned circumference coating layer is disposed.

In the honeycomb filter 3000 shown in FIG. 29, a shape of the cells 2 is quadrangular. However, the shape of the respective cells 2 in the respective honeycomb segments 64 is not limited to the quadrangular shape, and the shapes of the cells in the hitherto described honeycomb filters of the first embodiment to the tenth embodiment are employable.

(4) Manufacturing Method of Honeycomb Filter

Next, description will be made as to a method of manufacturing the honeycomb filter of the present invention. An example of the manufacturing method of the honeycomb filter of the present invention is a method including a step of preparing a honeycomb formed body, a step of forming plugging portions in open ends of cells, and a step of drying and firing the honeycomb formed body.

(4-1) Forming Step:

A forming step is a step of extruding a kneaded material obtained by kneading a forming raw material into a honeycomb shape to obtain the honeycomb formed body. The honeycomb formed body has partition walls which define cells extending from a first end face to a second end face, and a circumferential wall formed to surround an outermost circumference of the partition walls. A part of a honeycomb structure constituted of the partition walls corresponds to a honeycomb structure body. In the forming step, the forming raw material is initially kneaded to obtain the kneaded material. Next, the obtained kneaded material is extruded, thereby obtaining the honeycomb formed body in which the partition walls and the circumferential wall are monolithically formed.

It is preferable that the forming raw material is obtained by adding a dispersing medium and an additive to a ceramic raw material. Examples of the additive include an organic binder, a pore former, and a surfactant. An example of the dispersing medium is water. As the forming raw material, there is usable a material similar to a forming raw material used in a heretofore known honeycomb filter manufacturing method.

An example of a method of kneading the forming raw material to form the kneaded material is a method in which a kneader, a vacuum pugmill or the like is used. The extrusion can be performed by using an extruding die in which slits corresponding to a sectional shape of the honeycomb formed body are formed. For example, as the extruding die, it is preferable to use a die in which there are formed slits corresponding to the shapes of the cells in each of the hitherto described honeycomb filters of the first embodiment to the tenth embodiment.

(4-2) Plugging Step:

A plugging step is a step of plugging open ends of the cells to form the plugging portions. For example, in the plugging step, the open ends of the cells are plugged with a material similar to the material used in manufacturing the honeycomb formed body, to form the plugging portions. The method of forming the plugging portions can be performed in conformity with the heretofore known honeycomb filter manufacturing method.

(4-3) Firing Step:

A firing step is a step of firing the honeycomb formed body in which the plugging portions are formed, to obtain the honeycomb filter. The obtained honeycomb formed body may be dried with, for example, microwaves and hot air, before the honeycomb formed body in which the plugging portions are formed is fired. Alternatively, for example, the firing step of firing the honeycomb formed body is initially performed before the plugging portions are formed, and then, the above-mentioned plugging step may be performed to a honeycomb fired body obtained in the firing step.

A firing temperature in firing the honeycomb formed body can suitably be determined in accordance with a material of the honeycomb formed body. For example, when the material of the honeycomb formed body is cordierite, the firing temperature is preferably from 1380 to 1450° C. and further preferably from 1400 to 1440° C. Furthermore, it is preferable that the firing time is from about 4 to 6 hours as a time to keep the highest temperature.

EXAMPLES

Hereinafter, the present invention will further specifically be described in accordance with examples, but the present invention is not limited to these examples.

Example 1

To 100 parts by mass of cordierite forming raw material, 0.5 parts by mass of pore former, 33 parts by mass of dispersing medium and 5.6 parts by mass of organic binder were added, mixed and kneaded to prepare a kneaded material. As the cordierite forming raw material, alumina, aluminum hydroxide, kaolin, talc and silica were used. Water was used as the dispersing medium, a water absorbable polymer having an average particle diameter of 10 to 50 μm was used as the pore former, methylcellulose was used as the organic binder, and dextrin was used as a dispersing agent.

Next, the kneaded material was extruded by using a predetermined die, to obtain a honeycomb formed body in which a cell shape was substantially quadrangular and an overall shape was a round pillar shape.

Then, the honeycomb formed body was dried in a hot air drier. As drying conditions, the drying was performed at 95 to 145° C.

Next, plugging portions were formed in the dried honeycomb formed body. Specifically, a mask was initially applied to an inflow end face of the honeycomb formed body to cover inflow cells. Afterward, an end portion of the masked honeycomb formed body was immersed into a plugging slurry, to charge the plugging slurry into open ends of outflow cells which were not masked. Afterward, also as to an outflow end face of the honeycomb formed body, the plugging slurry was charged into open ends of the inflow cells by a method similar to the above method. Then, the honeycomb formed body in which the plugging portions were formed was further dried with the hot air drier.

Next, the dried honeycomb formed body was fired. As firing conditions, the honeycomb formed body was fired at 1350 to 1440° C. for 10 hours, thereby preparing a honeycomb filter of Example 1.

In the honeycomb filter of Example 1, a thickness of partition walls was 300 μm. A shape of cells was a shape in which corner portions of a quadrangular shape were formed into a curved shape of a curvature radius of 20 μm. Table 1 shows the thickness of the partition walls and the cell shape, in a column of “cell structure”. It is to be noted that Table 1 simply shows a polygonal shape as a shape in which corner portions of the polygonal shape are formed in a curved shape in a column of “cell shape”. Additionally, the curvature radius was measured by the following method. Initially, an inflow end face and an outflow end face of the honeycomb filter were imaged by using an image measuring instrument, for example, “VM-2520 (tradename)” manufactured by Nikon Corporation. Next, images of the imaged inflow end face and outflow end face were analyzed, thereby obtaining a curvature radius of each of the corner portions of the cells. In Example 1, curvature radiuses of 20 regions of the inflow end face and 20 regions of the outflow end face were measured, and an average value of the radiuses was considered as the curvature radius of the corner portions of the cells. In Example 1, the curvature radius of the corner portions of the cells was 20 μm.

In the honeycomb filter of Example 1, a shape of a cross section perpendicular to an axial direction was round, and a honeycomb structure body had a first cell row 15 and a second cell row 16 as shown in FIG. 4. A diameter of the inflow end face of the honeycomb filter was 266.7 mm, and a length (a total length) from the inflow end face to the outflow end face was 304.8 mm. Table 1 shows a shape of the honeycomb filter of Example 1 in columns of “sectional shape”, “diameter” and “total length”.

Table 2 shows a width P1 (mm) of the first cell row and a width P2 (mm) of the second cell row in the honeycomb filter of Example 1. Furthermore, Table 2 shows a value of “100−(P1/P2×100)” in a column of “P1, P2 ratio (%)”. Table 2 shows a value of “(P1+P2)/2” in a column of “average (mm) of P1 and P2”. Table 2 shows a value of a curvature radius R of the corner portions of the cells in a column of “curvature radius R (μm)”. Table 2 shows a value of “(R/1000)/((P1+P2)/2)×100” in a column of “X (%)”. The “X (%)” in Table 2 is a value represented by Equation (2) in the present description. Furthermore, Table 2 shows a cell structure in the honeycomb filter of each of the examples and comparative examples in a column of “cell structure”. For example, when the table shows FIG. 4 in the column of “cell structure”, it is indicated that the manufactured honeycomb filter has the cell structure shown in FIG. 4.

TABLE 1 Cell structure Thickness of Long Short Total partition walls Sectional Dia. dia. dia. length Porosity Material (μm) Cell shape shape (mm) (mm) (mm) (mm) (%) Example 1 Cordierite 300 Quadrangular Round 266.7 — — 304.8 52 Example 2 Cordierite 300 Quadrangular Round 266.7 — — 304.8 52 Example 3 Cordierite 300 Quadrangular Round 266.7 — — 304.8 52 Example 4 Cordierite 254 Quadrangular Round 143.8 — — 203.2 48 Example 5 Cordierite 254 Quadrangular Round 143.8 — — 203.2 48 Example 6 Cordierite 300 Quadrangular Round 143.8 — — 254.0 58 Example 7 Cordierite 300 Quadrangular Round 143.8 — — 254.0 58 Example 8 Cordierite 406 Quadrangular Round 190.5 — — 254.0 65 Example 9 Cordierite 406 Quadrangular Round 190.5 — — 254.0 65 Example 10 Cordierite 300 Quadrangular, Round 172 — — 177.8 52 octagonal Example 11 Cordierite 300 Quadrangular, Round 172 — — 177.8 52 octagonal Example 12 Cordierite 203 Quadrangular, Elliptic — 228.6 137.2 203.2 58 octagonal Example 13 Cordierite 203 Quadrangular, Elliptic — 228.6 137.2 203.2 58 octagonal Example 14 Cordierite 356 Quadrangular, Round 266.7 — — 254.0 65 octagonal Example 15 Cordierite 356 Quadrangular, Round 266.7 — — 254.0 65 octagonal Example 16 SiC 254 Quadrangular, Round 143.8 — — 177.8 41 octagonal Example 17 SiC 254 Quadrangular, Round 143.8 — — 177.8 41 octagonal Example 18 Cordierite 254 Hexagonal Round 172 — — 177.8 52 Example 19 Cordierite 254 Hexagonal Round 172 — — 177.8 52 Example 20 Cordierite 300 Hexagonal Round 143.8 — — 203.2 65 Example 21 Cordierite 300 Hexagonal Round 143.8 — — 203.2 65 Example 22 Cordierite 300 Quadrangular Round 143.8 — — 203.2 65 Example 23 Cordierite 300 Quadrangular Round 143.8 — — 203.2 65 Example 24 Cordierite 254 Quadrangular, Round 266.7 — — 304.8 65 octagonal Example 25 Cordierite 254 Quadrangular, Round 266.7 — — 304.8 65 octagonal

TABLE 2 P1 P2 P1, P2 ratio Average of P1 and P2 Curvature radius X (mm) (mm) (%) (mm) (μm) (%) Cell structure Example 1 1.40 1.47 4.8 1.435 20 1.4 FIG. 4 Example 2 1.10 1.47 25.2 1.285 20 1.6 FIG. 4 Example 3 0.78 1.47 46.9 1.125 20 1.8 FIG. 4 Example 4 1.42 1.47 3.4 1.445 50 3.5 FIG. 8 Example 5 1.05 1.47 28.6 1.26 50 4.0 FIG. 8 Example 6 1.41 1.47 4.1 1.44 50 3.5 FIG. 10 Example 7 0.90 1.47 38.8 1.185 50 4.2 FIG. 10 Example 8 1.75 1.80 2.8 1.775 100 5.6 FIG. 12 Example 9 0.95 1.80 47.2 1.375 100 7.3 FIG. 12 Example 10 1.43 1.47 2.7 1.45 80 5.5 FIG. 14 Example 11 0.85 1.47 42.2 1.16 80 6.9 FIG. 14 Example 12 1.40 1.47 4.8 1.435 50 3.5 FIG. 16 Example 13 1.05 1.47 28.6 1.26 50 4.0 FIG. 16 Example 14 1.40 1.47 4.8 1.435 100 7.0 FIG. 18 Example 15 1.00 1.47 32.0 1.235 100 8.1 FIG. 18 Example 16 1.42 1.47 3.4 1.445 70 4.8 FIG. 20 Example 17 1.15 1.47 21.8 1.31 70 5.3 FIG. 20 Example 18 1.43 1.47 2.7 1.45 50 3.4 FIG. 22 Example 19 0.95 1.47 35.4 1.21 50 4.1 FIG. 22 Example 20 1.34 1.37 2.2 1.355 100 7.4 FIG. 24 Example 21 1.10 1.37 19.7 1.235 100 8.1 FIG. 24 Example 22 1.40 1.47 4.8 1.435 100 7.0 FIG. 4, FIG. 26 Example 23 1.00 1.47 32.0 1.235 100 8.1 FIG. 4, FIG. 26 Example 24 1.42 1.47 3.4 1.445 100 6.9 FIG. 14, FIG. 27 Example 25 1.20 1.47 18.4 1.335 100 7.5 FIG. 14, FIG. 27

Examples 2 to 25

A cell structure, a sectional shape, a shape of a circumference and the like were changed as shown in Table 1 and Table 2, and honeycomb filters of Examples 2 to 25 were prepared. Here, FIG. 30 is an enlarged plan view of an enlarged part of an inflow end face, schematically showing the honeycomb filters of Examples 22 and Example 23. FIG. 31 is an enlarged plan view of an enlarged part of an outflow end face, schematically showing the honeycomb filters of Examples 22 and 23. In a honeycomb filter 1100 shown in FIG. 30 and FIG. 31, constituent elements similar to those of the honeycomb filter shown in FIG. 4 are denoted with the same reference numerals, and the description is omitted.

In Examples 16 and 17, as a material to prepare the honeycomb filter, silicon carbide (SiC) was used. The honeycomb filters of Examples 16 and 17 are honeycomb filters of segmented structures.

As to the honeycomb filters of Examples 1 to 25, evaluations were performed as to “pressure loss”, “soot leakage” and “general judgment” by the following methods. Table 3 shows the result.

(Pressure Loss)

Initially, a PM containing gas was generated by using a PM generator described in JP-A-2007-155708. Additionally, light oil was used as fuel of the PM generator. The PM containing gas generated from this PM generator was introduced from an inflow end face side of the honeycomb filter, and soot was deposited on the surfaces of the partition walls of the honeycomb filter. Then, in a state where the PM containing gas flowed at a flow rate of 10 Nm³/min and at 200° C., a pressure difference between the inflow end face and the outflow end face was obtained when soot was deposited in an amount of 1 g/L. The pressure difference obtained in this manner was considered as “a pressure loss value of the honeycomb filter”. Then, when the measured pressure loss value was compared with a pressure loss value of an evaluation standard mentioned below, a honeycomb filter in which a pressure loss decrease of 5% or more and less than 10% was seen was evaluated as “B”, and a honeycomb filter in which a pressure loss decrease of 10% or more was seen was evaluated as “A”. Furthermore, a honeycomb filter in which a pressure loss decrease was less than 5% or in which the pressure loss increased was an evaluated as “C”. In the evaluation of the pressure loss, the evaluation “A” or the evaluation “B” was a pass.

In the evaluation of the pressure loss, evaluation standards are as follows.

In Examples 1 to 3 and Comparative Examples 1 to 3, Comparative Example 1 is the evaluation standard.

In Examples 4 and 5 and Comparative Examples 4 and 5, Comparative Example 4 is the evaluation standard.

In Examples 6 and 7 and Comparative Examples 6 and 7, Comparative Example 6 is the evaluation standard.

In Examples 8 and 9 and Comparative Examples 8 and 9, Comparative Example 8 is the evaluation standard.

In Examples 10 and 11 and Comparative Examples 10 and 11, Comparative Example 10 is the evaluation standard.

In Examples 12 and 13 and Comparative Examples 12 and 13, Comparative Example 12 is the evaluation standard.

In Examples 14 and 15 and Comparative Examples 14 and 15, Comparative Example 14 is the evaluation standard.

In Examples 16 and 17 and Comparative Examples 16 and 17, Comparative Example 16 is the evaluation standard.

In Examples 18 and 19 and Comparative Examples 18 and 19, Comparative Example 18 is the evaluation standard.

In Examples 20 and 21 and Comparative Examples 20 and 21, Comparative Example 20 is the evaluation standard.

In Examples 22 and 23 and Comparative Examples 22 and 23, Comparative Example 22 is the evaluation standard.

In Examples 24 and 25 and Comparative Examples 24 and 25, Comparative Example 24 is the evaluation standard.

(Soot Leakage)

Initially, as to the honeycomb filter of each example, a hot vibration test was carried out by the following method. Initially, a ceramic mat which was not thermally expandable was wound around a circumferential surface of the honeycomb filter. Next, the honeycomb filter around which the ceramic mat was wound was stored in two divided stainless steel (SUS430) can bodies, and then, the can bodies were welded, to store the honeycomb filter in the can body. Hereinafter, the can body in which the honeycomb filter is stored will be referred to as “the can body for the test”. Next, the can body for the test was attached to a hot vibration test device, and a burning gas of propane was supplied from the hot vibration test device into the can body for the test. The burning gas was supplied at a gas temperature of 900° C. at maximum in the inflow end face of the honeycomb filter, and a gas flow rate was set to 2.5 Nm³/min. Furthermore, heating and cooling were repeated at an interval of 20 minutes to provide a heat cycle. Next, in a state where the above burning gas was continuously supplied into the can body for the test, vibration was applied to this can body in a direction perpendicular to an extending direction of the cells of the honeycomb filter. As conditions of the vibration applied to the can body, vibration of 40 G was applied at 150 Hz for 10 hours. Afterward, the can body for the test was rotated as much as 90° around a central axis of the honeycomb filter. The above operation was repeated four times in total. Therefore, a test time was 10 hours×4 times, i.e., 40 hours in total.

In the evaluation of soot leakage, the above-mentioned hot vibration test was carried out, and then, soot was deposited in an amount of 4 g/L in the honeycomb filter by use of the PM generator used in the evaluation of the pressure loss, to confirm leakage of the soot from the honeycomb filter. When the soot leakage from the honeycomb filter was not confirmed, the evaluation was “A”. When soot leakage from one region was confirmed in the honeycomb filter, the evaluation was “C”. When soot leakage from two or more regions was confirmed in the honeycomb filter, the evaluation was “D”. In the evaluation of the soot leakage, the evaluation “A” was a pass.

(General Judgment)

When the honeycomb filter satisfied passing criteria in both of the evaluation of the pressure loss and the evaluation of the soot leakage, the result was a pass. Table 3 shows “OK”. When the honeycomb filter did not satisfy the passing criteria in at least one of the evaluation of the pressure loss and the evaluation of the soot leakage, the result was a failure. Table 3 shows “NG”.

TABLE 3 Evaluation Pressure loss Soot leakage General judgment Example 1 B A OK Example 2 A A OK Example 3 A A OK Example 4 B A OK Example 5 A A OK Example 6 B A OK Example 7 A A OK Example 8 B A OK Example 9 A A OK Example 10 B A OK Example 11 A A OK Example 12 B A OK Example 13 A A OK Example 14 B A OK Example 15 A A OK Example 16 B A OK Example 17 A A OK Example 18 B A OK Example 19 A A OK Example 20 B A OK Example 21 A A OK Example 22 B A OK Example 23 A A OK Example 24 B A OK Example 25 A A OK

Comparative Examples 1 to 25

A cell structure, a sectional shape, a shape of a circumference and the like were changed as shown in Table 4 and Table 5, and honeycomb filters of Comparative Examples 1 to 25 were manufactured. Also as to the honeycomb filters of Comparative Examples 1 to 25, evaluations were performed as to “pressure loss”, “soot leakage” and “general judgment”. Table 6 shows the result.

TABLE 4 Cell structure Thickness of Long Short Total partition walls Sectional Dia. dia. dia. length Porosity Material (μm) Cell shape shape (mm) (mm) (mm) (mm) (%) Comparative Cordierite 300 Quadrangular Round 266.7 — — 304.8 52 Example 1 Comparative Cordierite 300 Quadrangular Round 266.7 — — 304.8 52 Example 2 Comparative Cordierite 300 Quadrangular Round 266.7 — — 304.8 52 Example 3 Comparative Cordierite 254 Quadrangular Round 143.8 — — 203.2 48 Example 4 Comparative Cordierite 254 Quadrangular Round 143.8 — — 203.2 48 Example 5 Comparative Cordierite 300 Quadrangular Round 143.8 — — 254.0 58 Example 6 Comparative Cordierite 300 Quadrangular Round 143.8 — — 254.0 58 Example 7 Comparative Cordierite 406 Quadrangular Round 190.5 — — 254.0 65 Example 8 Comparative Cordierite 406 Quadrangular Round 190.5 — — 254.0 65 Example 9 Comparative Cordierite 300 Quadrangular, Round 172 — — 177.8 52 Example 10 octagonal Comparative Cordierite 300 Quadrangular, Round 172 — — 177.8 52 Example 11 octagonal Comparative Cordierite 203 Quadrangular, Elliptic — 228.6 137.2 203.2 58 Example 12 octagonal Comparative Cordierite 203 Quadrangular, Elliptic — 228.6 137.2 203.2 58 Example 13 octagonal Comparative Cordierite 356 Quadrangular, Round 266.7 — — 254.0 65 Example 14 octagonal Comparative Cordierite 356 Quadrangular, Round 266.7 — — 254.0 65 Example 15 octagonal Comparative SiC 254 Quadrangular, Round 143.8 — — 177.8 41 Example 16 octagonal Comparative SiC 254 Quadrangular, Round 143.8 — — 177.8 41 Example 17 octagonal Comparative Cordierite 254 Hexagonal Round 172 — — 177.8 52 Example 18 Comparative Cordierite 254 Hexagonal Round 172 — — 177.8 52 Example 19 Comparative Cordierite 300 Hexagonal Round 143.8 — — 203.2 65 Example 20 Comparative Cordierite 300 Hexagonal Round 143.8 — — 203.2 65 Example 21 Comparative Cordierite 300 Quadrangular Round 143.8 — — 203.2 65 Example 22 Comparative Cordierite 300 Quadrangular Round 143.8 — — 203.2 65 Example 23 Comparative Cordierite 254 Quadrangular, Round 266.7 — — 304.8 65 Example 24 octagonal Comparative Cordierite 254 Quadrangular, Round 266.7 — — 304.8 65 Example 25 octagonal

TABLE 5 P1 P2 P1, P2 ratio Average of P1 and P2 Curvature radius X (mm) (mm) (%) (mm) (μm) (%) Cell structure Comparative 1.47 1.47 0.0 1.47 0 0.0 FIG. 4 Example 1 Comparative 1.45 1.47 1.4 1.46 20 1.4 FIG. 4 Example 2 Comparative 1.40 1.47 4.8 1.435 0 0.0 FIG. 4 Example 3 Comparative 1.47 1.47 0.0 1.47 50 3.4 FIG. 8 Example 4 Comparative 1.43 1.47 2.7 1.45 0 0.0 FIG. 8 Example 5 Comparative 1.47 1.47 0.0 1.47 50 3.4 FIG. 10 Example 6 Comparative 1.39 1.47 5.4 1.43 0 0.0 FIG. 10 Example 7 Comparative 2.00 1.80 −11.1 1.9 100 5.3 FIG. 12 Example 8 Comparative 1.78 1.80 1.1 1.79 5 0.3 FIG. 12 Example 9 Comparative 1.48 1.47 −0.7 1.475 80 5.4 FIG. 14 Example 10 Comparative 1.35 1.47 8.2 1.41 0 0.0 FIG. 14 Example 11 Comparative 1.46 1.47 0.7 1.465 50 3.4 FIG. 16 Example 12 Comparative 1.45 1.47 1.4 1.46 0 0.0 FIG. 16 Example 13 Comparative 1.49 1.47 −1.4 1.48 100 6.8 FIG. 18 Example 14 Comparative 1.20 1.47 18.4 1.335 0 0.0 FIG. 18 Example 15 Comparative 1.46 1.47 0.7 1.465 70 4.8 FIG. 20 Example 16 Comparative 1.30 1.47 11.6 1.385 2 0.1 FIG. 20 Example 17 Comparative 1.48 1.47 −0.7 1.475 50 3.4 FIG. 22 Example 18 Comparative 1.35 1.47 8.2 1.41 0 0.0 FIG. 22 Example 19 Comparative 1.37 1.37 0.0 1.37 100 7.3 FIG. 24 Example 20 Comparative 1.00 1.37 27.0 1.185 2 0.2 FIG. 24 Example 21 Comparative 1.47 1.47 0.0 1.47 70 4.8 FIG. 4, FIG. 26 Example 22 Comparative 1.45 1.47 1.4 1.46 0 0.0 FIG. 4, FIG. 26 Example 23 Comparative 1.48 1.47 −0.7 1.475 50 3.4 FIG. 14, FIG. 27 Example 24 Comparative 1.15 1.47 21.8 1.31 0 0.0 FIG. 14, FIG. 27 Example 25

TABLE 6 Evaluation Pressure loss Soot leakage General judgment Comparative Example 1 C D NG Comparative Example 2 C A NG Comparative Example 3 A D NG Comparative Example 4 C A NG Comparative Example 5 A C NG Comparative Example 6 C A NG Comparative Example 7 A C NG Comparative Example 8 C A NG Comparative Example 9 C C NG Comparative Example 10 C A NG Comparative Example 11 A C NG Comparative Example 12 C A NG Comparative Example 13 C D NG Comparative Example 14 C A NG Comparative Example 15 A D NG Comparative Example 16 C A NG Comparative Example 17 A C NG Comparative Example 18 C A NG Comparative Example 19 A D NG Comparative Example 20 C A NG Comparative Example 21 A D NG Comparative Example 22 C A NG Comparative Example 23 C D NG Comparative Example 24 C A NG Comparative Example 25 A C NG

(Result)

The honeycomb filters of Examples 1 to 25 satisfied passing criteria in both of the evaluation of the pressure loss and the evaluation of the soot leakage, and a result of “OK” was obtainable in the general judgment. On the other hand, the honeycomb filters of Comparative Examples 1 to 25 did not satisfy the passing criteria in at least one of the evaluation of the pressure loss and the evaluation of the soot leakage, and a result of “NG” was obtained in the general judgment. Specifically, in the honeycomb filters of Comparative Examples 1 to 25, when a value of “P1, P2 ratio (%)” of Table 5 was less than 2.0%, the result of the evaluation of the pressure loss was a failure. Furthermore, in the honeycomb filters of Comparative Examples 1 to 25, when a value of “X (%)” of Table 5 was less than 0.4%, the result of the evaluation of the soot leakage was a failure.

A honeycomb filter of the present invention is utilizable as a filter to trap particulate matter in an exhaust gas.

DESCRIPTION OF REFERENCE NUMERALS

1, 21 and 41: partition wall, 2, 22 and 42: cell, 2 a, 22 a and 42 a: inflow cell, 2 b, 22 b and 42 b: outflow cell, 3: circumferential wall, 4, 24 and 44: honeycomb structure body, 5, 25 and 45: plugging portion, 6: corner portion, 11, 31 and 51: inflow end face, 12 and 32: outflow end face, 15, 35 and 55: first cell row, 16, 36 and 56: second cell row, 64: honeycomb segment, 65: bonding layer, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100, 2000, 2100, 2200 and 3000: honeycomb filter, P1: width (the width of the first cell row), and P2: width (the width of the second cell row). 

What is claimed is:
 1. A honeycomb filter comprising: a honeycomb structure body having porous partition walls arranged to surround a plurality of cells extending from an inflow end face to an outflow end face to form through channels for a fluid, and a plugging portion disposed to plug either one of end portions of each of the cells on the side of the inflow end face or the side of the outflow end face, wherein the honeycomb structure body has a plurality of cell rows in which two or more cells are linearly arranged along one direction, in a cross section of the honeycomb structure body which is perpendicular to an extending direction of the cells, the plurality of cell rows include a first cell row and a second cell row, the first cell row is a cell row constituted of inflow cells in which the plugging portions are arranged in end portions on the outflow end face side and which are opened on the inflow end face side, the second cell row is a cell row of the cells linearly arranged along the one direction and including outflow cells in which the plugging portions are arranged in end portions on the inflow end face side and which are opened on the outflow end face side, a width P1 (mm) of the first cell row and a width P2 (mm) of the second cell row satisfy a relation of Equation (1) mentioned below, in the cross section perpendicular to the extending direction of the cells, each of the cells has a polygonal shape of which corner portions are formed in a curved shape of a curvature radius R, and the width P1 (mm) of the first cell row, the width P2 (mm) of the second cell row and the curvature radius R (μm) satisfy a relation of Equation (2) mentioned below: 2≤100−(P1/P2×100)≤50, and  Equation (1): 0.4≤(R/1000)/((P1+P2)/2)×100≤20.  Equation (2):
 2. The honeycomb filter according to claim 1, wherein an average value of the width P1 of the first cell row and the width P2 of the second cell row is from 0.5 to 2.7 mm.
 3. The honeycomb filter according to claim 1, wherein the width P1 of the first cell row is from 0.3 to 2.7 mm.
 4. The honeycomb filter according to claim 2, wherein the width P1 of the first cell row is from 0.3 to 2.7 mm.
 5. The honeycomb filter according to claim 1, wherein the width P2 of the second cell row is from 0.7 to 2.7 mm.
 6. The honeycomb filter according to claim 4, wherein the width P2 of the second cell row is from 0.7 to 2.7 mm.
 7. The honeycomb filter according to claim 1, wherein in the cross section perpendicular to the extending direction of the cells, a ratio N2/N1 of the number N2 of the second cell rows to the number N1 of the first cell rows is from 1/4 to 4.0.
 8. The honeycomb filter according to claim 6, wherein in the cross section perpendicular to the extending direction of the cells, a ratio N2/N1 of the number N2 of the second cell rows to the number N1 of the first cell rows is from 1/4 to 4.0.
 9. The honeycomb filter according to claim 1, wherein the second cell row is a cell row in which the inflow cells and the outflow cells are mixed.
 10. The honeycomb filter according to claim 8, wherein the second cell row is a cell row in which the inflow cells and the outflow cells are mixed.
 11. The honeycomb filter according to claim 1, wherein the second cell row is a cell row constituted of the outflow cells.
 12. The honeycomb filter according to claim 8, wherein the second cell row is a cell row constituted of the outflow cells.
 13. The honeycomb filter according to claim 1, wherein in the cross section perpendicular to the extending direction of the cells, the first cell rows are arranged on both sides of the second cell row, respectively.
 14. The honeycomb filter according to claim 10, wherein in the cross section perpendicular to the extending direction of the cells, the first cell rows are arranged on both sides of the second cell row, respectively.
 15. The honeycomb filter according to claim 12, wherein in the cross section perpendicular to the extending direction of the cells, the first cell rows are arranged on both sides of the second cell row, respectively.
 16. The honeycomb filter according to claim 13, wherein in the cross section perpendicular to the extending direction of the cells, the first cell rows and the second cell rows are alternately arranged in a direction perpendicular to the respective rows.
 17. The honeycomb filter according to claim 14, wherein in the cross section perpendicular to the extending direction of the cells, the first cell rows and the second cell rows are alternately arranged in a direction perpendicular to the respective rows.
 18. The honeycomb filter according to claim 15, wherein in the cross section perpendicular to the extending direction of the cells, the first cell rows and the second cell rows are alternately arranged in a direction perpendicular to the respective rows.
 19. The honeycomb filter according to claim 1, comprising two or more regions having different constitutions of cell rows in the cross section perpendicular to the extending direction of the cells, wherein the honeycomb structure body is present in at least a part of the regions.
 20. The honeycomb filter according to claim 1, comprising a plurality of honeycomb structure bodies, wherein each of the honeycomb structure bodies is constituted of a pillar-shaped honeycomb segment, and side surfaces of a plurality of honeycomb segments are bonded to one another by a bonding layer.
 21. The honeycomb filter according to claim 1, wherein the plurality of cells include cells having a hexagonal or an octagonal shape. 